Method of manufacturing a magnet core having an approximately rectangular hysteresis loop



2,905,641 TURING A MAGNET CORE HAVING AN p 22, 1959 c. J. ESVELDT ET AL METHOD OF MANUFAC APPROXIMATELY RECTANGULAR HYSTERESIS L Filed Dec. 20, 1954 INVENTORS CORNELIS JACOBUS ESVELDT EVERT WILLEM GOR TER ' AGENT United States Patent METHOD OF MANUFACTURING A MAGNET CORE HAVING AN APPROXIMATELY REC- TANGULAR HYSTERESIS LOOP Cornelis Jacobus Esveldt and Evert Willem Gorter, Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N .Y., a corporation of Delaware Application December 20, 1954, Serial No. 476,532

Claims priority, application Netherlands December 22, 1953 2 Claims. (Cl. 25262.5)

Magnet cores having an approximately rectangular hysteresis loop are of importance for various uses. This kind of cores is used inter alia for so-called magnetic memories (cf. for example W. N. Papian, Proceedings of the I.R.E., April 1952, pages 475 to 478, and D. R. Brown and E. Albers-Schoenberg, Electronics, April 1953, pages 146 to 149). Such magnetic memories are used inter alia in counting machines and automatic pilots. A further use is made of these cores in magnetic switches.

The invention will be explained in connection with the accompanying drawing in which Figs. 1 and 2 show portions of hysteresis loops of a ferromagnetic material.

The measure to which the shape of the hysteresis loop approaches that of a rectangle may be expressed quantitatively in various ways. A conventional measure may be the quotient a B cl In order to explain the meaning of the said quotient reference is made to Fig. 1, which shows diagrammatically part of a saturation magnetisation curve. In this figure B designates the remanent inductance and B the inductance at which the hysteresis loop just closes. In practice it is often not easy to measure B with great accuracy. However, an approximately correct value of B may be readily found by taking the average of the inductances subsequent to partial magnetisation and partial demagnetisation (with intermediate saturation), the two inductances being measured at the same field strength, which is chosen to be such that the said in ductances differ from one another more than 1% but less than 3%. This was carried out with the measurements in accordance with the present invention; for these measurements use was made of a ballastic galvanometer (cf. Bozorth: Ferromagnetism, page 843). If reference is made herein to the quotient this is assumed to be measured at an annular magnet core having a constant section of the ferromagnetic material along the entire periphery of the ring, having an outer diameter of not more than 1.6 times the inner diameter.

The extent to which the shape of the hysteresis loop approaches that of a rectangle may also be expressed by means of the so-called squareness ratio (R,),,,,,,,. For the meaning of this magitude reference is made to the aforesaid literature. For completeness sake a short explanation follows with reference to Fig. 2, which also shows diagrammatically part of a magnetisation curve, relating to a case in which the demagnetisation started before the magnetic saturation had been reached. The magnitude (R is defined as follows:

2,905,641 Patented Sept. 22, 1959 eam) max The quotient B (-1/2Hm) B m) is a function of the maximum field strength H applied, It is found that this quotient has a maximum for a given value of H which differs-mostly little from the coercivity H This maximum value of the quotient is desig nated by the symbol (Rp The measurements of B and B( 1/2Hm) required to determine (R may be performed with the aid of a ballistic galvanometer. The measuring objects are in this case also annular magnet cores having a constant section of the magnetic material throughout the periphery of the ring and an outer diameter of not more than 1.6 times the inner diameter. With the use of ferromagnetic materials having an approximately rectangular hysteresis loop we are mostly concerned with alternating currents of high frequency, so that it is necessary to restrict as far as possible the occurrence of eddy currents. With the use of ferromagnetic alloys this may be obtained to a certain extent by constructing the magnet core from relatively insulated, very thin layers of the ferromagnetic material. However, it is often extremely difiicult to compose cores having an approximately rectangular hysteresis loop from very thin layers. Consequently, with these high frequenoies it is advantageous and with higher frequencies it is even necessary to use magnetically weak, ferric oxide containing materials having spinel structure, since these substances have by nature a very low electrical conductivity.

For the serviceability of the magnet core concerned in magnetic memories and magnetic switches, it is furthermore an essential condition that the coercivity H should be low (preferably not higher than 10 oersteds and preferably even lower than 5 oersteds), since otherwise the electromagnetic losses would be too high.

In accordance with the invention it has now been found that magnet cores having an approximately rectangular hysteresis loop, in which the conditions and/or (R,),,,,,,, 0.6 and H 4 oersteds are fulfilled may be obtained by manufacturing them from a material consisting mainly of at least one compound of the formula:

Example A mixture of copper oxide, CuO, manganese carbonate, MnCO and iron oxide, Fe O is ground in alcohol for five hours and then preheated in air at 900 C. for one hour. Subsequent to cooling the reaction product is ground again in alcohol for two hours, after which the ground product is moulded to form a ring. This ring is heated at about 1350" C. in oxygen for two hours.

By varying the ratio of the quantities of copper oxide and manganese carbonate in the starting material, annular cores of different compositions are obtained. Of some of these magnet cores, the following table indicates the composition, the value of the quotient the value of (Rg and the value of H Composition i (Rog... H,

0110.05 Mums F8204 0. 70 O. 65 l. Cum MU FQ204 O. 70 O. 70 1. 0 011 .15 fln ss F6204- 0. 75 O. 75 1. 0110.1 M1103 F9204 O. 70 O. 60 1. 2 0110.1 LInm F9204- 0. 80 0.75 l. 0 C110 r M1114 F6204- 0.75 0. 70 1. 2 Gun is Mun. F6204. 0. 75 0. 75 1. 2 C110 15 1 1111.15 F8204- 0. 60 0. 60 1. 3 0110.2 MUM F8204- O. 75 O. 70 1. 2 CD04 Mnm F8204 0.70 0.70 1.4

What is claimed is:

1. A ferromagnetic ferrite having a substantially square hysteresis loop consisting essentially of a composition having the formula in which x is between 0.05 and 0.2 and y is less than 0.7, said ferrite having a coercive force of less than 4 oersteds, and at least one of the following properties: (a) Br/B greater than 0.7, and (b) (R greater than 0.6, said ferrite being obtained by firing in an atmosphere consisting essentially of oxygen at a temperature of about 4 1350 to 1400" C. a finely-divided mixture of copper oxide, manganese oxide, and ferric oxide in proportions corresponding to said formula.

2. A method of manufacturing a ferromagnetic ferrite having a substantially square hysteresis loop, said ferrite having a coercive force of less than 4 oersteds and at least one of the following properties: (a) B /B greater than 0.7, and (b) (Rg greater than 0.6, comprising the steps of forming a mixture of copper oxide, manganese oxide and ferric oxide corresponding to the formula in which x is between 0.05 and 0.2, and y is less than 0.7, and heating said mixture in an atmosphere consisting essentially of oxygen at a temperature of about 1350 to 1400 C. for about 2 hours.

References Cited in the file of this patent UNITED STATES PATENTS 2,715,109 Albers-Schoenberg Aug. 9, 1955 2,818,387 Beck et al Dec. 31, 1957 FOREIGN PATENTS 671,788 Great Britain May 7, 1952 697,219 Great Britain Sept. 16, 1953 OTHER REFERENCES Physica, No. 6, June 1936, pages 481-2. 

1. A FERROMAGNETIC FERRITE HAVING A SUBSTANTIALLY SQUARE HYSTERESIS LOOP CONSISTING ESSENTIALLY OF A COMPOSITION HAVING THE FORMULA 